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v3.25.3

Retroactive reinsurance contracts - Narrative (Detail) - USD ($) $ in Billions | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Retroactive Reinsurance [Member] |  |
Effects of Reinsurance [Line Items] |  |
Deferred charge assets on retroactive reinsurance contracts | $ 8.3 | $ 8.8

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- Definition Deferred charges assets on reinsurance assumed. + References No definition available. + Details
Name: | brka_DeferredChargeAssetsOnReinsuranceAssumed
Namespace Prefix: | brka_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_EffectsOfReinsuranceLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_CededCreditRiskAxis=brka_RetroactiveReinsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |